Carrier-current signaling system



- 1 619,085 March 1 ,1927. H NYQUIST CARRIER CURRENT SIGNALING SYSTEM Filed Feb. 29, 1924 3 Sheets-Sheet 1 1700+ 425- at 0 /700+ M55140 L) [[700 I N VEN 7i0R I2 By /W 5 A TTORNE Y March 1 1927. 1,619,085

H. NYQUIST CARRIER CURRENT SIGNALING SYSTEM Filed Feb. 29, 1924 s Sheebs-Sheet 2 INVENTOR zms-m-woa) i ATTORNEY March 1 1927. 1,619,085

H. NYQUIST CARRIER CURRENT SIGNALING SYSTEM Filed Feb. 29, 1924 5 Sheets-Sheet 3 INVEN TOR A TTORNE Y Patented Mar. 1, 1927.-

, UNITED STATES PATENTHOFFICE.

HARRY NYQUIST, OF JACKSON HEIGHTS, NEW YORK, ASSIGNOR T AMERICAN TELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF N EW YORK.

CARRIER-CURRENT SIGNALING SYSTEM.

Application 111 February 89, 1924. Serial No. 696,050.

An object of my invention is toprovide a new and improved system for the transmission of a plurality of messages on a slngle circuit. Another object of my inventlon 1s to provide for accurate and efi'ectlve synchronization of the apparatus at the sendmg and receiving stations in a multiplex carrier current signaling system. Another ob%e ct of my invention is to rovide for defimte y d stinguishing the di erent carrier frequencies over a wide f uency range. These and various other ob ects of my invention Wlll become apparent on consideration of the specific example which I have chosen to Illustrate the invention and which I now roceed to disclose in the following speci cation,-

taken with the accompanying drawings. It will be understood that this disclosure relates to this particular example of the in- 2 vention and that the scope of the invention is to be determined by the appended claims. Referrin to the drawings, Figure 1 is a diagram 0% a transmitting station, Fig. 2

is a diagram for a corresponding recelving 2 station, Fig. 3 is a diagram of a sending network, and Fig. 4 is a diagram of a receiving network.

At the sending station shown in Fig. 1, the constant speed motor PM drives ten alternating current generators G which may be inductor alternators. These generate currents of frequencies 170 cycles apart so that with the first generator givingv 425 cycles per 'second, the next gives up to 425+9X1 0:19.55 cycles per'second. From each of these generators G (with one exception presently to be noticed),. conductors lead in multiple to three sending net- 4 messages.

It will be seen that there would be 30 of these sending networks S in Fig. 1, except that two of them, the third and the thirteenth from the, top, are omitted for a purpose 425+170=595 c cles per second, and so on works S. One of these networks 'is shown which will be explained presently. The respective output currents from these sending networks S go through sending filters F whose output terminals are connected in parallel to the respective conductor pairs 11, 12 and 13. The currents gathered in conductors 11 are passed through the sending filter 'F,, which passes fre uencies 425-(1 to 1955-1-11, where d is ha f of the band width for each of the filters F Evidently, d has a value somewhat less than half of 170.

An oscillation generator 0 is provided, whose output frequency is as nearly as practicable 1700 cycles per second.. Its output current of frequency 1700 goes to the modulator M,, where it is combined with the currents of frequencies within the range from 425d to 1955+d in the conductors 12. The output from the modulator M goes to the filter F',, which passes the upper side band of frequencles, that is, from 17 00+425-d to 1700+1955-I-d.

The output from the oscillator 0 also goes to the frequency doubler FD and its output goes through the filter F which passes the frequency 3400 to the modulator M Here, the 3400 frequency is combined with the currents gathered in the conductors 13, and the corresponding filter F, passes the upper side band of frequencies, namely, those from 3400+425-d to 3400+1955+d..

The output currents from the three filters F,, F, and F", go to the line L, which may be a loaded line with amplifying repeaters 90. at suitable points. Transmission on this line is only one way, and the line may be one pair of a four-wire system.

At the receiving station shown in Fig. 2, the currents coming in on the line L are 95 separated into three frequency ran es by the respective filtersv F F and F ese being band-pass filters with ran es corresponding res ctively to those of t e filters F,, F, an F, at the sending end. Undersome circumstances the filters F, and F, may be omitted. It will be understood. that com- 'ing' in over the line L are 30 carrier currents, of WlllCh 28 are modulated in such a ductors 21 lead by multiple branches to the filters F each of band width 2d and each corresponding to a single carrier current and to one of the sending filters F To receive the output from each of the 30 filters F is a receiving network R, except that for two of the thirty channels, such networks are omitted, as will be explained presv ently.

Each receiving network R also receives from a local source a pure sine wave alternatlng current of the corresponding carrier frequency is present as a, pure sine wave,

lator DM is the pure frequency 2465. This 1s passed by the filterjF to the demodulator frequency. and reception is by the homodyne .DM where it is combined with the fremethod. Each such receiving network may have four relays and four respective detectors, all as shown in Fig. 4:. Each of the four detectors D D D and D responds to one, and one only, of the four messages 7 carried on the carrier current of the corresponding frequency, as determined by the respective key K K K or K at the sending end. PR, and'PR are polar relays and NR and NR, are marginal neutral relays.

It is important that accurate frequency and phase relations shall be maintained between the sending station of Fig. 1 and the receiving station of Fig. 2. The generators G at the receiving station are driven by the synchronous motor SM, which receives its current from a power tube generator P The input current that controls the frequency of the power tube generator P is the received carrier current of frequency 765 cycles per second. It will be seen that the receiving network for this frequency is omitted and that the current goes directly from. the filter F to thepower tube. P At the sending end, the corresponding network is also omitted so that the current of this frequency 765 cycles per second goes on the line as a pure sine wave current, unmodulated by any message.

. in relation to the receiving system of Fig. 2, we have thus far traced only the output of the filter F in the output'conductors 21. The outputs from the other two filters'F' and F 3 on the respective conductors 22 and 23 go to demodulators DM and DM in which they are combined with locally generated currents of respective frequencies 1700 and 3400 cycles per second. The 1700 cycle current at the receiving station is generated by a tube P In the drawing, the output of the tube 1? is also marked 00 as well as 1700 to facilitate discussion of how this output frequency is determined.

It will be seen that at the sending station the sending network has been omitted at the quency 7 65 received directly through the thirdfilter F from the topin Fig. 2. The output from the demodulator DM, comprises a component of the frequency which is passed by the filter F and goes therefrom to control the frequency of the power tube P Thus, it is determinedthat the-output from power tube P, has the frequency 1700, in other words, 0:1700. -Accordingly, in the demodulator DM 1700 is subtracted from the frequencies coming in from the line, and the resulting frequencies passed by the corresponding filters F range from 425-d to 1955-l-d. p

The 1700 cycle output from the power tube P also goes to the frequency doubler FD 'and thence through the filter F giving a frequency of 3400 for the demodulator DM From what has gone before, it will readily be seen that the frequencies in the conductors 23 range from 3400+425d .to 3400+1955+d and are all reduced by 3400 and then delivered to the corresponding filters F; and receiving networks B.

This explains how the tube P is made to supply the proper frequency during the operation, but does not account'for its starting initially. To insure this the tube P is equipped with a feed back-circuit such as is common in vacuum tube oscillators and which is so adjusted that when there is no current delivered from'F the tube oscillates gently at approximately 1700 cycles. This is enough to start the cycle described above and when it is once started the frequency is determined by the frequencies delivered from the line.

In the system which is here disclosed it will be seen that I make use of phase discrimination at all frequencies within the range of the system. Phase discrimination becomes increasingly difficult as the frequency is increased on-account of the difficulty of providing a synchronous source at the receiving end. Thisdifiiculty is overcome by the system shown, in which the synchronous motor SM at the receiving end and the power tube 1?, at the receiving end are kept accurately in step respectively with the one component of the output of the demodumotor M at the sending end and the oscillation generator 0 at the sending end.

It Wlll be seen that the filters F at the sending end and F at the receiving end are of'narrow band width. When a filter of narrow band width is employed for a high frequency, it is somewhat diflicult to secure accurate adjustment. For example, it is easier to adjust a filter toaband width of 170 when the mean frequency is 1955 than when the means frequency is 3400+1955. It will be seen that in the system here disclosed, the filters mentioned F and F 4 run no higher in mean frequency than 1955 at the sending end and likewise at the receiving end. At each end there are three groups of filters, with ten in each group, and the groups are alike. Thus, the difiiculty is obviated of attempting to secure adjustment for the narrow band width filters at high mean frequencies.

I claim:

1. The method of enerating and transmitting a plurality o currents of different respective frequencies, which consists in generating the currents of lower frequency in primary generators and delivering them to at least three multiple branch circuits and in certain of the multiple branches from each generator applying them to modulate other currents of different respective frequency values and separating out by filters the modulation product currents of frequency higher than those generated at the outset, and superposing the currents in all said multiple branches in a transmission line.

2. The method of multiplex carrier current transmission, which consists in modu-. lating low frequency alternating currents, more than two of each frequency, according to respective messages, applying one set of these currents of different frequency directly to the line and applying other sets to modulate other currents different from each other in frequency and then filtering out the higher frequency components and applying them also to the line.

3. In combination, a. plurality of alternating current generators of different frequency, at least three branch circuits from each, means to modulate one set of currents according to messages to be sent and to put the modulated currents on a transmisslon line, means to modulate other similar sets similarly and then to step them up infrequency of different amounts and also put them on the same line. I

4. A transmission line, a plurality of generators of comparatively low frequency a1- ternating current, at least three branch circuits from each such generator, means to modulate one set of currents of different frequency in one set of branch circuits .according to messages to be sent and put such currents on the line, means similarly to modulate the currents in other similar sets of branch circuits, and means further to appl such currents collectively to modulate other currents of different frequencies, and filter out from the modulation product currents, a higher range of frequencies than that delivered by the generators and put them also on the line.

5. In combination, alternating current .enerators of a variety of comparatively low requencies, at least three multiple branch circuits from each, similar means .to modulate these currents in each branch ,'a transmission line, means-to put one set of modulated currents correspondin generators directly on the to step up each other similar set of modulated currents to respective different higher frequencies and also put them on .the line.

6. In a multiple-x carrier current transto the various. ne', and means mission system, a transmission line, at least three receiving filters to separate thevarious modulated carrier currents into as many groups with a plurality of different frequencies in each group, means to step the currents down to lower frequency in each group. of higher frequency, and respective detectors for the respective carrier channels at these lower frequencies.

- 7. The method of multiplex carrier current transmission, which consists in gener ating currents of various definitely related frequencies,'modulati ng them in accordance with messages to be transmitted, generating another current, modulating this with the output message bearing currents, filtering and transmitting a range of frequencies higher than those generated initially, also transmitting tw'o unmodulated frequencies,

and at the receiving end applying one of these to determine the local generation of a set of currents corresponding in frequency to those initially generated at the sending end andalso at the receiving end applying the other unmodulated current to determine the frequency of a local generator corresponding in frequency to the single generator at the transmittin end.

8. The method of multiplexcarrier current transmission, which consists in modulating 'low frequenc alternating currents, at least three of eac frequency, according to respective messages, applying one set of these currents of difierent frequency directly to the line and applying the other such sets to modulate other different frequency currents and then filtering out the higher frequency components and applying them also to the line, and at the receiving end separating these sets of currents by filters and steppingv down the frequencies of the currents of higher frequency and applying all said currents to respective detectors.

9. In combination, a plurality of alter- .nating current generators of different frequency, at least three respective branch cirtransmission line, means to modulate each other similar set similarly and then to step them up in frequency by different amounts and also put them on the same line, and at the receiving. end filters to separate the said sets of currents, means to step down the currents of the set of higher frequency, and respective detectors for the currents.

10. The method of signaling, which consists in simultaneously stepping up each of a plurality of signalingv ands in the frequency spectrum from substantlally the same level by respectively different amounts to different levels and then combining the resultant bands at such different levels.

11. The methodiof signaling, which consists in transmitting a band of frequencies corresponding to a signal but elevated in the frequency spectrum with respect to the normal signaling range, transmitting with said band other signalin bands likewise elevated but to different leve s of the frequency spectrum, filtering said bands at different levels into different circuits, and stepping down simultaneously all said bands to the same orignal normal signaling range.

12. The method of multiplex telegraph signaling, which consists in generating carrier currents of various frequencies, distributing such currents to a plurality of groups of sending networks, each frequency of current being distributed to a respective network in each group, modulating these currents in said networks each according to four messages distinguished by phase and by magnitude, superposing and transmitting the output currents from one group, stepping up the frequencies of the output currents of the other groups by a different amount for each such group and superposing and transmitting these currents of stepped-up frequency along with the others, and at the receiving end separating the groups by filtering, further separating the frequencies of the said one group byfiltering and delivering the filtered output currents to respective receiving networks, steppin down the frequencies of the other groups y the amounts by which they were stepped up at the sending end, separating the fre uencies of these groups by filtering and de 'vering the filtered output-currents to other respective receiving networks.

13. The method of multiplex telegraph signaling, which consists in generating carrier currents of various frequencies, distributing such currents to a plurality of groups of sending networks, each frequency of current being distributed to a respective network in each group, modulating these currents in said networks each according to four messages distinguished by phase and by mag-.

nitude, superposing and transmitting the output currents from one group, stepping up the frequencies of the output currents of the other groups .by a different amount for each such group and superposing and transmitting these currents of stepped-up frequency along wit-h the others.

14. The method of carrier current signaling, which consists in message-modulating respectively each of at least three currents of the same low frequency, simultaneously stepping all but one of them up to different levels of frequency, transmitting them, separating them at the receiving end by filters according to the friquency levels, stepping down those of higher frequency level to the original level, and detecting the messages in each corresponding message channel.

' In testimony whereof, I have signed my name to this specification this 27th day of February, 1924.

. HARRY NYQUIST. 

